Hardware__Display Screens

Refresh Rate

Most LCD screens & touch displays use a 60Hz refresh rate. However, larger monitors especially those for gaming will use 75Hz or greater refresh rates, and the new iPad Pro can throttle up to 120Hz. However, it is important to note that the physical refresh rate is an upper bound and often the OS actual refresh rate will be slightly below this. For example on a 75Hz Acer xr382cqk running on Mac OS, the measured screen refresh is 74.4Hz instead of 75. On a google pixel C, the screen refresh is 59.16Hz instead of 60. These measurements can be made by running window.requestAnimationFrame without any drawing commands (dummy loop). Knowing this actual refresh rate can save a lot of trouble when testing the frame rate of a particular image display implementation in your behavioral paradigm.

// Estimate max software fps
var lasttime = null
var elapsedSinceLastFrame = [];
var nframes = 0
var dtScreen = 0;
function dummyLoop(timestamp){
	if (!lasttime) lasttime = timestamp
	elapsedSinceLastFrame[nframes]=(timestamp-lasttime)
	lasttime=timestamp
	nframes=nframes+1
  	if (nframes < 20){
  		window.requestAnimationFrame(dummyLoop)
  	}
  	else {
  		for (var i=10; i<=nframes-1; i++){
			dtScreen = dtScreen + elapsedSinceLastFrame[i]
  		}
  		dtScreen = dtScreen / (nframes - 10)
  	}
}
window.requestAnimationFrame(dummyLoop);

Image Sizing (placeholder)

DPI for tablets and smartphones

264 dpi - Samsung Galaxy Tab S2 9.7
281 dpi - Nexus 9
287 dpi - Samsung Galaxy S 10.5
308 dpi - Google Pixel-C
359 dpi - Samsung Galaxy S 8.4
458 dpi - Apple iPhone X
538 dpi - Google Pixel 2 XL